constant of proportionality(n = noun.quantity) factor of proportionality - the constant value of the ratio of two proportional quantities x and y; usually written y = kx, where k is the factor of proportionality;
is a kind of constant, factor
has particulars: h, planck's constant

boltzmann's constant, constant, constant lambert, constant of gravitation, constant quantity, cosmological constant, dissociation constant, equilibrium constant, factor of proportionality, gas constant, gravitational constant, hubble constant, hubble's constant, law of constant proportion, leonard constant lambert, planck's constant, proportionality, rydberg constant, solar constant, time constant, universal gas constant, universal gravitational constant